JPH0512188B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a device for steering both the front wheels and the rear wheels in a four-wheeled vehicle such as an automobile, that is, by steering the front wheels, which are steering wheels, the rear wheels as well as the front wheels are steered. This invention relates to improvements to wheel steering devices.

Conventionally, steering devices in four-wheeled vehicles steer only the front wheels, and the rear wheels tend to steer actively, although they do some toe-in or toe-out depending on the driving situation, regardless of the steering of the front wheels. I haven't gotten used to it. However, recently, a four-wheel steering device has been proposed in which both the front wheels and the rear wheels are steered (for example, Japanese Patent Laid-Open No. 55-91458), and research on this type of device is being carried out.

According to the four-wheel steering system, convenient maneuvering that was previously impossible and driving with improved steering performance are possible depending on various driving conditions of the vehicle. for example,
When maneuvering a vehicle at extremely low speeds, such as parallel parking or parking in a garage, by steering the rear wheels in the opposite direction to the front wheels (this is called anti-phase), it is possible to significantly change the direction of the vehicle. This makes it possible or easy to park in narrow spaces, which was previously impossible or extremely difficult. Also, U
This is also advantageous when turning, since the minimum turning radius can be made small. Furthermore, by steering the rear wheels in a phase opposite to that of the front wheels, the difference between the inner wheels can be minimized or eliminated, which is advantageous when turning a narrow corner. Also,
When steering a vehicle at such extremely low speeds, if the rear wheels are steered in the same direction as the front wheels (this is called in-phase), it is possible to move the entire vehicle in parallel, making it easier to park or park the vehicle. It is often useful when

On the other hand, when changing lanes while driving at medium to high speeds, if four-wheel steering is performed in the same phase, lateral force is applied to the front and rear wheels at the same time, making it possible to change lanes smoothly without phase lag, thereby suppressing yawing. This allows you to change lanes at high speed without fear. Furthermore, when cornering, the direction of the vehicle can be effectively changed by steering the rear wheels in opposite phases.

Furthermore, when driving straight ahead, if the rear wheels are steered in a direction that counteracts the effect of external disturbances such as crosswinds, stable driving can be maintained against external disturbances, and stable high speeds can be achieved. It is also possible to obtain straightness.

Additionally, even if the front wheels are kept at a constant steering angle during a turn and the vehicle accelerates or decelerates, the rear wheels' steering angle changes in response to the acceleration or deceleration to ensure stable turns without deviating from the course. It can also be done. In other words, in conventional vehicles, the steering characteristics are adjusted to slightly understeer in order to maintain straight-line stability, and when accelerating during a turn, there is a tendency for the vehicle to deviate outward from the course. By doing so, the deviation can be corrected and stable turning can be realized.

In terms of comfort, it is possible to obtain a smaller minimum turning radius with the same wheelbase, so the wheelbase can be increased, and in addition to this, the actual steering angle of the front wheels can be reduced. It has many advantages, including the ability to experiment with new designs.

As described above, four-wheel steering has many practical advantages and is extremely useful.

Regarding this four-wheel steering, various specific configurations have been proposed so far to effectively steer the rear wheels. For example, a system in which four-wheel steering is performed in opposite phases at low speeds and in the same phase at high speeds (Japanese Patent Application Laid-open No. 1983-1999)
91457), the same phase when the steering angle of the front wheels is small, and the opposite phase when it is large (Japanese Patent Application Laid-open No. 1983-
No. 5270) The rear wheels are steered in proportion to the steering angle of the front wheels only when the steering angle of the front wheels is below a predetermined range, and when the steering angle of the front wheels is above a predetermined range, the rear wheels are steered regardless of the steering angle of the front wheels. Fixed angle (Unexamined Japanese Patent Publication No. 1983-
163969) etc. are known.

These four-wheel steering devices, when the vehicle speed is low,
Or, based on the empirical rule that when the front wheel steering angle is large, it is often necessary to change the direction of the vehicle significantly, and when the vehicle speed is high or the front wheel steering angle is small, it is often necessary to make a slight lateral movement. The rear wheels are always steered in the desired direction.

In such a four-wheel steering system, a controller is provided with a predetermined control pattern that determines the steering angle of the rear wheels according to the size of the steering angle of the front wheels and the vehicle speed, and the output of this controller is used to control the steering angle of the rear wheels. A rear wheel steering device is required to steer the vehicle. This rear wheel steering device uses a link mechanism that is mechanically linked to a steering device that steers the front wheels, or a hydraulic actuator that uses hydraulic pressure to steer the rear wheels based on a signal related to the front wheel steering angle. However, in practice, a device using a hydraulic actuator is preferable because it can obtain a larger steering force and perform smooth control. A vehicle that steers the rear wheels using an actuator in this manner is disclosed in, for example, Japanese Patent Application Laid-Open No. 11173/1983.

In an actual vehicle, it is preferable to use such a hydraulic actuator because it can obtain a large steering force, but the conventional rear wheel steering device described above uses a solenoid to control the control valve that is supposed to generate a large steering force. Since it is a large solenoid, it is necessary to generate a large force using a large solenoid. Particularly, when a neutral position biasing means is provided in the rear wheel steering device as a countermeasure against failure, it is necessary to generate an even larger force, resulting in a problem that the solenoid becomes extremely large.

Due to this problem, a large current is required, and the problem of heat generation due to the large size of the solenoid.
Various problems have arisen, such as decreased responsiveness, difficulty in fine-grained control, and decreased reliability, and improvements have been desired.

In view of these problems, the present invention provides a four-wheel vehicle that does not cause the above problems, has good responsiveness, enables detailed control, and is highly reliable, and enables rear wheel steering using a hydraulic actuator. The object of the present invention is to provide a steering device.

The four-wheel steering device according to the present invention includes a steering device that steers the front wheels, a hydraulic actuator that receives hydraulic pressure and strokes an actuating rod to steer the rear wheels, and a neutral position that urges the rear wheels to a neutral position. a first control valve that controls the amount and direction of hydraulic pressure supplied to the hydraulic actuator by displacement; a first hydraulic pressure generating means for supplying hydraulic pressure; a pilot hydraulic passage for displacing the first control valve by hydraulic pressure; a second control valve that controls hydraulic pressure acting on the first control valve and changes the displacement direction of the first control valve; and a second hydraulic pressure generator that supplies hydraulic pressure to the pilot hydraulic passage through the second control valve. It is characterized by comprising means.

In this way, the first control valve that controls the amount and direction of hydraulic pressure supply to the hydraulic actuator is
On the other hand, since it is controlled by hydraulic pressure that can generate a large force, it is possible to steer the rear wheels reliably without causing the problems described above, and it is also essential for four-wheel steering systems. A certain improvement in responsiveness and fine control can be achieved.

Hereinafter, the present invention will be explained in more detail with reference to the drawings.

Fig. 1 shows an embodiment of the four-wheel steering system of the present invention, Fig. 2 is a sectional view showing the details of the control valve, which is the main part, and Fig. 3 is a further enlarged view of the main part. FIG. Furthermore, Fig. 4A is a graph showing changes in the actual steering angle of the rear wheels, Fig. 4B is a graph showing changes in the rotation angle during steering wheel operation, and Fig. ₅ is a graph showing changes in the rotation angle when the steering wheel is operated, and Fig. 5 is a graph showing changes in the actual steering angle of the rear wheels. It is a graph showing the relationship of angle θ _R in one control mode of four-wheel steering.

The four-wheel steering system is a system that steers the front wheels 1, 1 by steering the steering wheel 3 in FIG. 1, thereby steering the rear wheels 2, 2 according to the steering angle of the front wheels 1, 1. The relationship between the front wheel turning angle θ _F and the rear wheel turning angle θ _R at this time is determined by a control mode as shown in FIG. 5, for example. In FIG. 5, broken lines V1, V2, and V3 indicate control patterns in the automatic control mode when the vehicle speed is high, medium, and low, respectively, and inflection points P1, P2, and P3 indicate the steering ratio θ _R / θ _F is the front wheel steering angle θ _F
indicates the point at which the steering ratio changes with respect to a change in the angle of change, and where the front wheel steering angle θ _F is smaller than this inflection point, the steering ratio θ _R /θ _F
is relatively large, and above this inflection point it remains unchanged or decreases as the front wheel steering angle θ _F increases. Further, this steering ratio θ _R /θ _F increases as the vehicle speed increases. Furthermore, when the vehicle speed is low (V3), when the front wheel steering angle θ _F becomes above θ _F ′, the rear wheel steering angle θ _R becomes negative, and antiphase steering is performed, and the steering angle θ increases at low speed. When _H is large, the rear wheels are steered in the opposite phase, making it possible to change the direction of the car significantly. In addition, in the embodiment shown in FIG. 5, in addition to the three types of control patterns V1, V2, and V3 described above, the rear wheel steering angle θ _R is set in the same phase as the front wheel steering angle θ _F increases regardless of the vehicle speed. Four-wheel steering is performed using two fixed modes: fixed mode X, which increases the amount, and fixed mode Y, which increases the amount in opposite phase. This is useful when parallel parking or parking in a garage, when you want to make sure to steer the rear wheels a lot to move the car diagonally horizontally or change direction with a small turning radius. In the above three types of automatic control patterns V1, V2, and V3, below the inflection point, the steering ratio θ _R /θ _F is made relatively large to eliminate phase delay in lane changes, etc., and improve responsiveness. On the other hand, above the inflection point, the steering ratio is made relatively small to improve cornering performance and maneuverability.

The control pattern shown in Figure 5 above is an example of a control pattern for four-wheel steering, and various other control patterns can be implemented, but in any case, the rear wheels respond sensitively when the front wheels are steered. There are times when you want it to be responsive, and times when it's better to have less responsiveness for stability. Fig. 4B shows changes in the rotation angle θ _H of the steering wheel 3 steered by the driver, which occurs when the driver suddenly turns the steering wheel, first turning the steering wheel abruptly, and then making a constant turn for a while. Indicates a condition to continue. At this time, the steering angle (actual steering angle) θ _R of the rear wheels 2, 2 is determined by the hydraulic actuator 2 as a value corresponding to the actual steering angle θ _R in FIG. 4A.
As shown with the actuation amount dt of 3 (Fig. 1),
It rises suddenly at first (A), then stabilizes in a wave-like manner (B).
At this time, the steeper the rising portion (A) is, the better, and the flatter the stable portion (B) is, the better. Therefore, it is desirable that a large hydraulic pressure differential be obtained at the start of steering corresponding to the rising portion (A), and that a small differential pressure be obtained thereafter. The differential pressure at the start of steering is calculated between the target rear wheel steering angle (the corresponding hydraulic actuator operation amount d) and the actual rear wheel steering angle at that point (the corresponding hydraulic actuator operation amount). It is preferable that the difference (d−dt) from the amount dt) is larger, and smaller as the difference (d−dt) is smaller, since a required amount of steering force can be obtained with the required sensitivity.

Hereinafter, embodiments of the present invention that satisfy this requirement will be described in detail with reference to FIGS. 1 to 3 and 6 to 8.

As shown in FIG. 1, in this embodiment, the front wheels 1, 1 and the rear wheels 2, 2 are mechanically separated, and the output of the front wheel turning angle sensor 4 detects the steering angle θ _H of the steering wheel 3. 4a is input to the controller 10 of the rear wheel steering device, and the rear wheels 2, 2 are steered by this input signal. As is well known, the front wheel steering device moves a rack 6 in the width direction of the vehicle using a pinion 5 fixed to a steering shaft 3A to which a steering wheel 3 is fixed, and tie rods 7 continuous to both ends of the rack 6. , 7, the knuckle arms 8, 8 of the left and right front wheels 1, 1 are rotated around their shafts 8a, 8a, thereby steering the front wheels 1, 1 left and right. That is, when the steering wheel 3 in the figure is rotated in the direction of the arrow (right), the steering shaft 3A is also rotated in the same direction, the pinion 5 is also rotated in the direction of the arrow, and the rack 6 is moved to the left. As a result, the left and right front wheels 1, 1's knuckle arms 8, 8 are rotated in the direction of the arrow via the tie rods 7, 7, and the front wheels 1, 1 are rotated to the right around the shafts 8a, 8a of the knuckle arms 8, 8. and steer to the right. At this time, the steering angle sensor 4 outputs an output signal 4a indicating that the steering wheel 3 has rotated to the right by an angle θ _H , and inputs this to the front wheel steering angle input 10A of the controller 10 of the rear wheel steering device.

The controller 10 is supplied with power by a power source 11, and in addition to the front wheel steering angle input 10A, the controller 10 has a vehicle speed input 10B connected to a vehicle speed sensor 12, and a feedback input 10C connected to a rear wheel steering angle sensor 13. The steering direction output 10D is connected to the solenoid 201 that controls the steering direction of the rear wheels, and the hydraulic pump motor is connected to the motor 22A of the hydraulic pilot pump 22 that controls the steering angle θ _R of the rear wheels. It has an output of 10E.

The hydraulic pilot pump 22 includes a pump 22B that discharges oil (hydraulic oil).
Control valve 2 that controls hydraulic actuator 23
Between this switching valve 202 and the pump 22B, an orifice path 20B is provided which short-circuits the oil outgoing path 20A and the oil return path 20C, and is equipped with an orifice 20b in the middle. An oil reservoir 203 is arranged.

The switching valve 202 has a valve portion consisting of two inlets connected to an oil outgoing path 20A and an oil return path 20C, and two outlets communicating with the inlets connected to the oil outgoing path 20A and an oil return path 20C.
2A and 202B are provided in parallel in a switchable manner, and by operating the solenoid 201, one of these two valve parts 202A and 202B is connected to the oil outgoing path 20A and the oil return path 20C. It's getting old. The two outlets of this valve 202 are connected to the right oil passage 2 of the control valve 24.
0D and the left oil passage 20E, and the right oil passage 20D and the left oil passage 20E communicate with the outgoing path 20A and the return path 20C via the valve 202.

Further, the controller 10 includes the control valve 2
Main pump motor output 10 is connected to the motor 21A of the main pump 21 that supplies oil (hydraulic oil) for driving the hydraulic actuator 23 to 4.
It is equipped with F. This main pump 21 includes a pump 21B that discharges oil, and this pump 21
B is connected to the hydraulic actuator 23 via a control valve 24. Disposed between the control valve 24 and the pump 21B are an oil outgoing path 20F, a drain 20G, and an oil return path 20H that is connected to the drain 20G via a reservoir 204 and returns to the pump 21B. The drain 20G is branched into two drain branch pipes 20g, 20g and connected to two drain ports of the control valve 24.

Details of the control valve 24 will be explained with reference to FIGS. 2 and 3. The control valve 24 has reaction force chambers 24A and 24 at both ends of the cylinder 242 by the piston 240.
B is formed in which a compression spring 241 is inserted.
R, 241L are provided so that the piston 240 is biased to the neutral position (the position shown in FIG. 2). The piston 240 has large diameter portions 240A and 240D at both ends.
The shaft 240a has a small diameter portion between them, and control portions 240B and 240C, which form a medium diameter portion, are provided at both ends and the center of the shaft 240a, spaced apart from each other. The inner wall of the cylinder 242 has a large diameter portion at a portion facing the control portions 240B, 240C, that is, a portion located around the control portions 240B, 240C when the piston 240 is in the neutral position. , 240C and the inner walls 242a, 242b (FIG. 3) of the cylinder 242 to form annular control chambers 24d, 24e. Between the shaft 240a of the piston 240 and the inner wall, there are a right chamber 24a, a central chamber 24b, and a left chamber 24c.
are formed in this order with control sections 240B and 240C sandwiched therebetween. The right ventricle 24a and the left ventricle 24c are connected to drain branch pipes 20g and 20g, respectively, and are connected to the central ventricle 24a.
4b communicates with the oil outgoing path 20F. control room 2
4d and 24e are the right oil passage L where the right control chamber 24d is connected to the right chamber 33A of the hydraulic actuator 23, and the left oil passage L where the left control chamber 24e is connected to the left chamber 23B of the hydraulic actuator 23.
are connected to each other.

The hydraulic actuator 23 is located on the central partition plate 23c.
The chamber is partitioned into a right chamber 23A and a left chamber 23B through the chamber, and springs 23a and 23b are housed in each chamber to urge the partition plate 23c to a neutral position. The partition plate 23c is fixed to the actuation rod 26, and the pressure difference (differential pressure) between the right chamber 23A and the left chamber 23B is
The actuating rod 26 is driven left and right by the actuating rod 26, and the knuckle arms 28, 28 of the rear wheels 2, 2 are moved to the shafts 28a, 28 through the tie rods 27, 27 connected thereto.
Rotate around 28a.

Now, the steering direction switching valve 202 switches the positive valve portion 202B to the oil outgoing path 20A and the oil return path 20A according to the signal from the output 10D of the controller 10.
C, the pressure in the right oil passage 20D becomes higher than the pressure in the left oil passage 20E, and the pressure in the right reaction force chamber 24A of the control valve 24 becomes higher than the pressure in the left reaction force chamber 24B. As a result, the piston 240 moves to the left against the force of the spring 241L in the left reaction force chamber 24B. FIG. 3 shows a state in which the piston 240 has moved to the left in this manner.

FIG. 3 shows the piston 240 moved slightly to the left. When the piston 240 moves to the left, the control units 240B and 240C of the piston 240
are shifted to the left from the control chambers 24d and 24e, respectively, so that the communication portion between the right control chamber 24d and the center chamber 24b becomes narrower, and the communication portion between the left control chamber 24e and the center chamber 24b becomes wider. Thereby, the pressurized oil sent from the main pump 21 is pressurized into the central chamber 24b, passes through a narrow communication section to the right control chamber 24d and a wide communication section to the left control chamber 24e, and then passes through the right chamber 24a,
It flows into the left ventricle 24c and returns to the reservoir 204 from the drains 20g, 20g. At this time, right control room 2
The right chamber 24a side of 4d is wide open, and the hydraulic passage is switched to the right oil passage 23R, and the left control chamber 24e is opened.
Since the left chamber 24c side is narrower to regulate the oil pressure, the flow rate of oil flowing through the right control chamber 24d is high, and the flow rate of oil flowing through the left control chamber 24e is slow. Therefore, according to Bernoulli's theorem, the right control room 2
The pressure in the left control chamber 24e is low, and the pressure in the left control chamber 24e is high. Therefore, the pressure in the right oil passage 23R to the hydraulic actuator 23 is low, and the pressure in the left oil passage 23L is high.

As a result, the right chamber 23 of the hydraulic actuator 23
The pressure in the left chamber 23B is low and the pressure in the left chamber 23B is high, the partition plate 23c is pushed to the left, the actuating rod 26 moves to the right, and the rear wheels 2, 2 are moved to the right via the tie rods 27, 27, as indicated by the arrows. It is steered to the right.

The steering speed of the rear wheels 2, 2 at this time is
Hydraulic actuator 23 corresponding to the target steering angle of 2
The position of the operating rod 266 (d) and the rear wheel 2 at that time,
The controller 10 responds to the difference (d-dt) between the positions (dt) of the actuating rod 26 corresponding to the two actual steering angles.
is determined. In other words, the controller 10 has the difference (d
-dt), the rotation speed of the motor 22A of the pilot pump 22 is increased (FIG. 6). The piston 2 of the control valve 24 depends on the rotation speed of the motor.
40 actuation amount, that is, the left and right reaction force chambers 24A, 24
The differential pressure of B is determined (FIG. 7), and this differential pressure determines the differential pressure between the left and right chambers 23A and 23B of the actuator 23 (FIG. 8). The rotation speed of the motor 22A is determined by the output 10E of the controller 10.

Note that this controller 10 can also be used to increase the rotational speed of the motor 22A of the pilot pump 22 when the vehicle speed V is low, that is, at low speed, thereby increasing the differential pressure in the reaction force chamber and the differential pressure in the actuator. It is possible. (6th,
(See Figures 7 and 8) In this way, by increasing the actuator differential pressure at low speeds, the steering force of the rear wheels can be increased at low speeds, and it is possible to assist with the steering force that tends to be insufficient at low speeds. .

As described in detail above, according to the four-wheel steering system of the present invention, the first control valve that controls the amount and direction of hydraulic pressure supply to the hydraulic actuator is
On the other hand, since it is controlled by hydraulic pressure that can generate a large force, there is no need for conventional control using large solenoids, and the various problems caused by this have been solved, and the rear wheels can be rotated reliably. Furthermore, it is possible to improve responsiveness and achieve fine control, which are essential in a four-wheel steering system.

[Brief explanation of the drawing]

Fig. 1 is a system diagram showing the entire four-wheel steering system according to an embodiment of the present invention, Fig. 2 is a sectional view of a control valve used in the main part thereof, Fig. 3 is an enlarged sectional view thereof, and Fig. 4A. Figure 4B is a graph showing the change in actual steering during rear wheel steering, Figure 4B is a graph showing the rotation angle of the steering wheel for front wheel steering, Figure 5
The figure is a graph showing an example of the four-wheel steering control mode.
Fig. 6 is a graph showing the relationship between the difference between the target steering angle and the actual steering angle of the rear wheels and the rotation speed of the pilot pump, and Fig. 7 is a graph showing the relationship between the above difference and the differential pressure in the reaction force chamber of the control valve. FIG. 8 is a graph showing the relationship between the above difference and the differential pressure of the actuator. 1... Front wheel, 2... Rear wheel, 3... Steering wheel, 4... Steering angle sensor, 5... Pinion, 6... Rack, 7, 27... Tie rod, 8, 28... Knuckle arm, 10... Controller, 11... Power supply, 12
...Vehicle speed sensor, 13...Feedback potentiometer, 20A, 20F...Oil outward path, 20B
...Orifice path, 20C, 20H...Oil return path,
20D...Right oil passage (pilot hydraulic passage),
20E...Left oil passage (pilot hydraulic passage),
20g...Drain, 201...Solenoid, 202...
Rear wheel steering direction switching valve (second control valve), 21...
Main pump (first hydraulic pressure generating means), 21A...main motor, 21B...pump, 22...pilot pump (second hydraulic pressure generating means), 22A...pilot motor, 22B...pump, 23...hydraulic actuator, 23A...right ventricle, 23B...Left ventricle, 23a,
23b...Spring (neutral position biasing means), 23
c...Partition plate, 23R...Right oil passage, 23L...Left oil passage, 24...Control valve (first control valve),
240...Piston, 24A...Right reaction force chamber, 24B...
Left reaction force chamber, 240A, 240D...Large diameter section, 240
B, 240C...Control unit, 240a...Axis, 24a...
Right ventricle, 24b...Central ventricle, 24c...Left ventricle, 24d...
Right control room, 24e...Left control room, 242a, 242
b...Inner wall.

Claims (1)

[Scope of Claims] 1. A steering device that steers the front wheels, a hydraulic actuator that receives hydraulic pressure and strokes an actuation rod to steer the rear wheels, and a neutral position biasing device that biases the rear wheels to a neutral position. a first control valve that controls the amount and direction of hydraulic pressure supplied to the hydraulic actuator by displacement; and a first control valve that controls the hydraulic pressure supplied to the hydraulic actuator through the first control valve. a first hydraulic pressure generating means for supplying the first hydraulic pressure; a pilot hydraulic passage for displacing the first control valve by hydraulic pressure; and a pilot hydraulic passage provided in the pilot hydraulic passage and controlling the first control according to the steering state of the front wheels. a second control valve that controls the hydraulic pressure acting on the valve and changes the displacement direction of the first control valve; and a second hydraulic pressure generating means that supplies hydraulic pressure to the pilot hydraulic passage through the second control valve. A four-wheel steering device for a vehicle, comprising: